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54 Cards in this Set

  • Front
  • Back
With digital sensors and plates, what do the xrays interact with?
electronic detectors
What has higher radiation sensitivity, digital or radiographic films?
digital sensors and plates have higher radiation sensitivity

radiographic film has low radiation sensitivity
Advantages of digital imaging
reduction in radiation by 60-90%

pt education

increased diagnosis

short exposure time

elimination of darkroom

elminate hazardous chemicals

remote consultaion capibility
What are disadvantages of digital imaging?
fear of change

no film in hand

trusting computers for storage

unknown life expectancy of sensor

initial set up cost
What is required components for digital imaging?
software and computer with analogue to digital converter (ADC)



Sensors or plates
How is digital imaging arranged?
in a matrix of rows and columns

each cell of the image matrix is called a pixel or picture element

each pixel has a row and column coordinates that identify its location in the matrix
Describe pixel size
it varies from 20-70 microns

the smaller the pixel the higher the cost BUT the greater the resolution
With digital imaging, what is analogue data converted into?
numerical data
What happens to each pixel of digital imaging during xray?
xray absorption generates voltage at each pixel
What does ADC consist of
sampling and quantification
small range of voltage values are grouped together as a single value
every sample is assigned a value
How is voltage of output signal measured during digital imaging?
it is measured and assigned a number from 0 (black) to 255 (white) according to the intensity of the voltage

this value stored in the computer represents the image
with digital imaging how many shades of gray can it translate?

how about with traditional xrays?

the human eye/
numerical assignments translated 256 shades of gray in digital imaging

traditional radiographs differentiated 16-25 shades of gray

the human eye can appreciate 32-64 shades of gray
the measure of small objects placed together
resolution of film, CCD sensors, and PSP
Film = 16-20 lp/mm

CCD = 8-10 lp/mm

PSP = 6-8 lp/mm

Film has the highest resolution and PSP has the lowest
With digital imaging what is used in place of film?
plates or sensors
2 ways to acquire direct image
1. sensors

2. PSP plates
What does PSP stand for?
photostimulable phosphor plates
2 types of sensors
1.CCD (charged couple device)

2.CMOS (complimentary metal oxide semiconductors)
how much less exposure do you get with digital sensors vs. D and E film?
get 50-80% less exposure with sensors
Thickness of digital sensors
2.2-8 mm they are rigid with round edges
describe CCD sensors
solid state detectors made up of thin wafer of silicon crystals arranged in a pixel

the exposure creates electron hole pairs (greater exposure, greater e-hole pairs)

e- are attracted to the positive potential and create charge pkts on each pixel

emage is read by transferring each row of pixel charge from one to the the next pixel and is transferred to a ADC

after sampling and quantification, the image is read
What should be used to increase xray absorption and effincy of CCD
layer of scintillating material (gadolinium oxybromide cmpds or cesium iodide) coated on the CCD or coupled to the surface by fiberoptics
detectors in CMOS
silicon based semiconductors
How are pixels read differently in CMOS than in CCD
in CMOS each pixel is isolated and is directly connected to a transistor

electron holes are produced and charge is transferred to the transistor directly to a small voltage

voltage is read by a frame grabber and then is stored and displayed as digital gray volume
Only company that makes CMOS sensor
What are some good things ahout sensors/
first wireless direct digital imaging

no need for scanning or processing

sensor instantly transmits images from mouth

cable free sensors allow mobility

hi level of image quality and reduced radiation exposure
What do PSP require?
What do PSP resemble?
intraoral film in size, thickness, and rigidity

more flexible than sensors
What phosphor do PSP plates use?
europium doped barium fluorohalide

the electrons in europium capture xray energy and are stored in metastable state
How are PSP plates image displayed?
PSP plates are scanned with a red laser light scanner (600nm) which causes the plates to release energy in green spectrum (300-500nm)

light from the PSP is conducted to photomultiplier tube via fiberoptics

photomultiplier tube converts light into electrical energy

voltage signal is quantified by ADC and stored and displayed as digital imaging
what is added to PSP to allow only green light to be detected?
a red filter at the photomultiplier tube is added to remove red light and only allow green light to be detected and converted into voltage
when should PSP be processed?
ASAD bc trapped e- are spontaneously released over time but PSP can be stored for 12-24 hrs and still retain ok image quality
Is red safe light ok for exposed PSP?
NO!!!!! bc PSP is most sensitive to red light spectrum
2 types of scan systems for PSP plates
1. stationary systems

2. rotating plate scans
How to erase and reuse PSP
PSP is exposed to bright light to eliminate the ghost image from prior exposure
ideal kVp for xray equiptment
60-70 kVp
what type of machine should CMOS and CCD be used with?
CMOS and CCD detectors should preferabley by used with DC type intraoral machines with 1/100 sec exposure intervals for shorter exposure time
What type of macine should PSP plates be used with?
older AC xray machine
what characteristic shoulc an xray generator have to be used with a solid state detector?
low kVp (lower that 70kVp)

low mA (less than 5mA)

accurate timer

timer capable of producing very short and accurate times

small focal spot

a DC circuit
describe image processing with digital images?
digital image can be altered by electronic image processing without making another exposure
What can be done to process and edit digital image processing?
contrast and brightness

image size

measurement of structures

image oritentation

reduce noise/sharpen/smooth





changes a small highlighted area to show trabeculae more clearly
digital subtractoin
two images of the same area taken at different intervals are required

shows the subtle differences between two images
average std digital image size
200-400 KB
image size of FMX
8 MB
image size of Pano
5 MB
image size of ceph
6-8 MB
describe teleradiology
need a dedicated telephone line

does 56 KB/sec
what computer hardware is needed for digital imaging in dental office
plenty of RAM
hard drive of 20 GB
56 kbps modem
back up devices
600 dpi with transparency adapter
color printer
what does DICOM stand for?
digital imaging and communications in medicine
Purpose of DICOM
standardizes digital image formates

images can be transferred to remote sites
DICOM compliant
system utilizes common file formats that are universally recognized